Polar-equatorial ionospheric currents driven by the region 2 field-aligned currents at the onset of substorms

Details Polar-equatorial ionospheric currents driven by the region 2 field-aligned currents at the onset of substorms Polar-equatorial ionospheric currents driven by the region 2 field-aligned currents at the onset of substorms

Sep 2011

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011jgra..11609217h&link_type=abstract

Journal of Geophysical Research, Volume 116, Issue A9, CiteID A09217

Physics

Ionosphere: Electric Fields (2712), Ionosphere: Equatorial Ionosphere, Ionosphere: Plasma Convection (2760), Magnetospheric Physics: Field-Aligned Currents And Current Systems (2409), Magnetospheric Physics: Substorms

Scientific paper

The dawn-to-dusk convection electric field increases during the growth phase of substorms, driving DP2 currents composed of two-cell current vortices in high latitude and leading to an increase in the eastward electrojet at the dayside dip equator (EEJ). During the expansion phase of substorms, electric field and currents are often reversed in direction to the normal DP2 currents at subauroral to equatorial latitudes when the convection electric field reduces abruptly. The reversed current at the dayside dip equator appears as a counterelectrojet (CEJ) and causes an equatorial enhancement of the negative bay in the afternoon sector. Conversely, the convection electric field increases during substorms as deduced from sawtooth events, causing an increase in the EEJ. In this study, by analyzing isolated substorms with magnetometer array data and SuperDARN (Super Dual Auroral Radar Network) convection maps, we deduce that the reversed electric field and currents develop at the subauroral-to-equatorial latitudes at the onset of substorms, while the convection electric field increases at auroral latitudes. These observations imply that both the region 1 and region 2 field aligned currents (R1 and R2 FACs) develop on the dayside concurrently with the current wedge responsible for the midlatitude positive bay at midnight. The substorm-associated R2 FACs are strong enough to cause the reversed current at the subauroral latitude and the CEJ at the equator. We also deduce that the dayside equatorial CEJ begins simultaneously with or even earlier than the midlatitude positive bay at midnight while the midlatitude positive bay onset is delayed by several minutes as the station departs from the midnight meridian. These observations suggest that the substorm begins with the intensification of the R2 FACs responsible for the equatorial CEJ.

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